In the simplest explanation possible, I will attempt to demonstrate explicitly how you can achieve a star trail image such as this. I will also briefly explain the reasoning for each part of the process. This step by step process may seem fairly strict, but like any artistic project, there will always be room for creativity.
Step 1: Choose the right environment. To achieve the most crisp and clear image, it's best to shoot in a cool and dry environment. To be honest, the reasoning for this involves some science that's pretty far over my head. Anyways, it's also integral that you choose a night/environment that features the lowest amount of light and cloud coverage. For this picture, I took the exposure during a "New Moon," where the moon is nearly invisible (Doesn't emit light). The weather conditions were also clear, dry, and around 22 degrees Fahrenheit. Lastly, this exposure was taken between the hours of 10 PM and 12 AM.
Step 2: Set up Equipment. Once the destination has been chosen and the perfect night has arrived, it's time to head out and get set up. There are a few integral components that must be added to an arsenal of camera equipment to achieve an image such as this. In addition to a DSLR camera these additional pieces include, a sturdy tripod, wide angle lens, remote shutter, flashlight, timer, warm clothes, and at least two hours hours of your time. The tripod will inevitably be necessary because the camera will be taking "long exposures," thus any camera shake from the photographer would ruin an image. A wide angle lens is not entirely necessary, but I personally appreciate pictures of the sky where a large portion of the sky is featured. The remote shutter will be used alongside the camera to automatically fire the camera's shutter continuously for an extended duration of time. Similarly to the wide angle lens, a flashlight is not integral but can be helpful when working with equipment where little light exists. Since the conditions will likely be cold for your shoot, definitely prepare yourself for the worst, dress warm! The last component refers to a minimum two hour window for the exposure. I will explain later, but most photographers would agree that a two hour exposure is the minimum period of time that will yield a star trail photograph.
Step 3: Set Exposure. From most of the reading I have done, many photographers seem to have varying opinions in regards to setting the camera's exposure settings properly before taking the photos necessary for achieving a star trail image. With this being said, there is a general consensus that these opinions all lead to. The first action that should be taken when setting the camera's exposure is to set the camera's dial to manual mode or "M," mode. This will allow for complete control of all of the exposure settings manually. The next action that should be taken is to set the camera's shutter release setting to "Continuous/Remote Control." Every DSLR will have a slightly different setting, but this setting in combination with the Remote Shutter Release cable will give the camera the ability to fire its shutter continuously at a fixed rate automatically for a specific duration of time. After this process is completed, you must then set the ISO, Focal Length, Aperture, and Shutter Speed. ISO of course refers to how sensitive the camera is to available light. In theory, since you will be shooting this project with very little light, one would think that a high ISO setting must be used. But a high ISO setting comes at the cost of a "noisy" or grainy image. It must also be understood that every camera performs differently at specific ISO settings, therefore it's best to learn how your camera performs before setting the ISO. With this being said, for this image I set the camera's ISO setting to 1600. The focal length refers to a calculation of the optical distance from the point where light rays converge to create a sharp image of the subject to the digital sensor at the focal plane of the camera. As I have mentioned previously, I feel that the most compelling star trail photography images are created with the use of a wide-angle lens. Wide-angle lenses typically feature focal lengths that range anywhere from 14mm-35mm. Although, this image was actually taken with an ultra-wide angle lens, because this lens features a focal length range of 10mm-22mm. As far as specifically setting the focal length, it's entirely up to you, but for this picture, I set the focal length to 10mm. The camera must also be set to manual focus, with the focus ring set to infinity. These two settings are necessary because most cameras will be unable to fire their shutter without a certain amount of available light with the auto-focus setting turned on. The aperture refers to a hole within the camera lens that serves as a passageway for light travel into the body of the camera. If an aperture is large, more light will hit the camera's sensor. Aperture also controls the "Depth of Field," which refers to the portion of a composition that appears to be in focus. If the aperture setting is small, such as F/11, the Depth of Field is considered large, where more of the composition will be in focus. On the flip side, if the aperture setting is large, such as F/2.0, the Depth of Field is considered small, where only a portion of the composition will be in focus. For the purpose of this photo, since I desired that a large portion of the image be in focus, in a low light setting, I set the aperture to F/5.6. The last of the exposure settings that stand as integral to achieve a photograph such as this refers to setting the camera's shutter speed. Shutter speed simply refers to the time interval between the camera's opening and closing of its shutter. Different star effects can be achieved with the utilization of variable camera shutter speeds, but for the purpose of this shoot, I chose a shutter speed of 30 seconds.
Step 4. Start shooting! I will apologize for the lengthiness of the previous step, but I feel that a step-by-step process in combination with an accompanying explanation paves the way for a valuable learning experience. Moving forward, once all of the camera exposure settings are dialed in, it's time to document the stars. As I have mentioned previously, the camera's shutter should be set to "Continuous/Remote Shutter." Position the camera to capture a desired composition, hold down the shutter release cable trigger, lock it into place, and let the camera do the rest of the work! Ultimately, if you follow all of the previous steps, you will have set the camera to take continuous pictures at a 30 second long exposure continuously, every 30 seconds, for two hours. After this two hour period is complete, around 170 images will have been taken depicting the same stars at varying locations in the night sky.
Step 5. Edit the Images. Like any photographic process, there are numerous ways in which the batch of photos can be edited to create one conglomerate star trail image. But since I appreciate simplicity and strategies that require a low-budget, I utilized the wonderful batch editing program known as Adobe Lightroom, ($9.99/month) in combination with StarStax. StarStax is a free program that serves as a fast multi-platform image stacking and blending software, which gives the user the ability to combine a series of photos into a single image while using various in-program blending modes. With this being said, once the selection of images are appropriately edited in Adobe Lightroom to a desirable level, the group can then be loaded into the StarStax program to be blended into one conglomerate image. Before completing this shot, I found a great video tutorial on YouTube that explains how to utilize the program StarStax to produce a stunning Star Trail photography image. The link to this video can be found here. StarStax Tutorial Video (Fast forward to 9:32 to arrive at the tutorial for the StarStax program.)
I hope that this step by step process will be helpful in achieving an image similar to the one that I captured myself. Of course, I am still an amateur photographer, so any of the information that I have provided should strictly be utilized as guidance. Additionally, in photography, some rules are meant to be broken! So get out there and start experimenting, good luck with the shoots!
